In the games

Marlon appears in Pokémon Black 2 and White 2 as the eighth and last Gym Leader that the player challenges. He is a big-hearted Pokémon Trainer who gives passionate advice. Marlon also seems to be a very relaxed and carefree man, as shown by his obliviousness as to who Team Plasma are and what they do. He asks the player if Team Plasma are bad people.

Marlon specializes in Water-type Pokémon. Upon defeating him, he will reward the player with a Wave Badge and TM55 (Scald). Outside of battle, Marlon is a fisherman who catches Water-type Pokémon which he would later use in future Gym battles.

Upon arriving in Humilau City, Marlon is absent from the Gym, and the player is sent to find him. The player meets Marlon just as they head north of the Gym, in which he returns to it and awaits a Gym battle. After the Gym battle, Marlon jumps into the ocean and swims away. Upon exiting the Gym, Hugh walks up and congratulates the player on gaining all eight of Unova's Gym Badges, and then their attention turns to Team Plasma, during which Marlon walks up and asks about them.

He heads off to the Seaside Cave to find the Plasma Frigate. Later on on Route 21, he is seen jumping off the Plasma Frigate after lowering the boarding plank, and then heads back to the Gym, leaving the player and Hugh to deal with Team Plasma.

Quotes

"Sup, you must be here to challenge the Pokémon Gym! I'm the Gym Leader, Marlon. Sorry to make you look for me, yo. I was swimmin' with the Pokémon, and it felt real good, so I kept goin' and goin'. I'll be waitin' in the Gym, 'K?"

"Hey, friends! Team Plasma's not botherin' me. They could be up to no good for reals, and… It's not my style to go around decidin' Team Plasma's bad without thinkin' 'bout it just 'cause everyone says so! But, eh, you're havin' trouble, so I've got to help out! That's what I want to do!"

"Listen, 'K. Believe in somethin'! Searchin' for stolen Pokémon is fine! Keepin' Unova from bein' iced over's fine too! It's all good. But think 'bout why you're doin' that. The strength of your beliefs is what gives you and your Pokémon power! I made some noise, so some people came out! Hey, be careful, 'K!"

National Gymquirer

Jingle: "Woo hoo! All right! It's 'The National Gymquirer'!"

Page: "That's right! We collect the hottest gossip about Gym Leaders seen around town! Here is today's letter. From someone going by the name MisterFisher! Thank yooou! 'Marlon was swimming the other day, and he just kept going faster until he shot out of the water and into the sky! That swimming style could completely dominate the world of swimming.' Hm... That is amazing, but nobody else can do that. Actually, can you even call jumping into the sky swimming? 'The National Gymquirer'! We eagerly await your letters!"

In the anime

Marlon in the anime

Marlon made his debut appearance in BW094, where Kotetsu battled him for his Gym badge and won.

Pokémon

Wailord

Wailord is used as a means of transport to take Marlon and his challengers to the Humilau City Gym.

Jellicent was the first Pokémon Marlon used against Kotetsu in their Gym battle. He battled Kotetsu's Ferrothorn, and after being defeated by Ferrothorn's Thunderbolt, his Ability activated, disabling the move.

Mantine was the second Pokémon Marlon used against Kotetsu in their Gym battle. It quickly knocked out Ferrothorn with a combination of Wing Attack, Bullet Seed, and Psybeam. Afterwards, Mantine faced Kotetsu's Samurott and was knocked out without landing an attack on it.

Trivia

Being at level 55, Marlon's Jellicent in Challenge Mode is the highest leveled Pokémon to be owned by a Gym Leader during the initial battle with them, tied with Giovanni's Nidoking and Rhydon in Yellow.

Marlon is the first Gym Leader since Chuck who only appeared in one episode of the anime.

According to the television, Marlon learned to jump by practicing with the Mantine that lived by his childhood home.